Tongs are presently used to engage vertically suspended sheets of glass which are moved through various treatment stations. The tongs are closed automatically by the weight of the sheet so as to firmly clasp the sheet along its upper edge. In one form of prior art device the tongs are connected to a yoke which is adjustably positioned on a carrying beam mounted to a handling trolley. An example of such a device is disclosed in U.S. Pat. No. 3,010,753. In order that the horizontal position of the yoke which supports the tongs may be varied, the support face of the carrying beam has a plurality of hollow recesses into which a bolt connected to the yoke may be screwed. The accuracy of the positioning of the tongs along the sheet of glass is determined by the distance between the various recesses into which the holding bolt is screwed.
In a further form of a handling device used to date, a supporting beam which forms a part of a transport trolley carries a toothed rack where a ring to which tongs are connected is placed in a desired position in a space between adjacent teeth of the toothed rack. Accuracy of positioning in such a device is determined by the spacing between the teeth of the rack. Such a device is disclosed in German Pat. No. 1,596,394.
It is desirable that tongs which support a sheet of glass be positioned in precise positions along the sheet and particularly when the sheet passes through a pressing station to undergo bending into a convex shape involving small radii of curvature. If the sheet to be bent is not precisely positioned in the pressing station, tolerances pertaining to a particular shape may not be obtained such that glass sheets will be rejected as not meeting quality control standards.
Further it is important that the tongs gripping a sheet of glass be precisely positioned in relation to the tools for bending the glass with the caveat that the more sharply the sheets are to be bent, the more important it is that the tongs be accurately placed. Even after pressing and bending of the sheet has taken place, that is when the molds are removed, the tongs must not exert a great amount of force on the sheet as the sheet could be bent out of shape. When multiple tongs are used to obtain a multiple suspension of a sheet, it is the usual procedure to suspend the tongs from a beam mounted to a trolley at particular points on the beam which lie directly above the center of gravity of the bent portions of the sheet. This demands extreme precision in placement of the tongs. Multiple engagement of tongs using this procedure is disclosed in German Patent Application Publication No. 1,596,394.
Structure used to date for positioning tongs onto beams or of attaching beams onto handling trolleys are of relatively rough construction. This is because the structures, the beams and the tongs are all subjected to large temperature fluctuations passing from an ambient temperature to temperatures in excess of 650.degree. C. Under such conditions, rugged heavy parts are required to withstand the temperature changes.
In apparatus used to date, it is difficult, if not impossible, to provide for easy, convenient and precise adjustment of the suspension tongs with respect to the handling trolley.
It is therefore an object of the invention to provide for an apparatus which will allow easy, convenient and precise positioning of suspension tongs with respect to a suspension beam and with respect to a handling trolley and where the structure of the apparatus is simple, rugged and sufficient to withstand extreme changes of temperature.